The subject matter disclosed herein relates to the art of electric machines and, more particularly, to a rotor lamination assembly for a permanent magnet electric machine.
Electric machines include a rotor that sets up a magnetic field. Electrical current passing though a stator is influenced by the magnetic field creating an electromotive force that causes the rotor to spin. Certain electric motors/generators employ permanent magnets in the rotor. The permanent magnets are mounted in magnet slots formed in the rotor which is typically formed from a plurality of laminations. Generally, the permanent magnets are mounted near an outside edge of the rotor, as close to the outside edge as possible, in order to maximize torque and minimize flux losses. Mounting the permanent magnets in this manner creates a thin bridge area between the magnet slots and the outside edge of the rotor.
During high speed operation, centrifugal forces on the rotor create stress in the thin bridge area. If operated at too high a speed, the stress can exceed the yield strength of the laminations. In such a case, the rotor could fail. Accordingly, there is a trade off between maximizing torque and high speed operation. That is, maximizing torque by mounting the permanent magnets as close to the outside edge of the rotor limits the overall operational speed of the electrical machine.